1. Field of the Invention
The present invention relates to a method of forming a thin film, and more particularly, to a method of forming an indium tin oxide thin film using a magnetron negative ion sputter source.
Although the present invention is suitable for a wide scope of applications, it is particularly suitable for forming an indium tin oxide thin film at a low temperature which has a high transmittance as well as a high electrical conductivity.
2. Discussion of the Related Art
An indium tin oxide (ITO) thin film has been widely used in optoelectronic devices, such as a solar cell, a liquid crystal display (LCD), and a flat panel display, due to its unique properties of a high transmittance in visible light region and a high electrical conductivity. A resistivity of the ITO thin film depends on a tin doping level and a concentration of oxygen vacancies. Also, its high optical transmittance stems from the high intrinsic band gap energy of 3.5 eV. The ITO thin film is normally deposited by the conventional magnetron sputtering using a ceramic target or by electron beam evaporation in a controlled oxygen ambient condition with heating a substrate or a post annealing at the temperature in the range of 300 to 400xc2x0 C.
For a color filter application in an LCD and a flat panel display, a substrate processing temperature is limited to below 250xc2x0 C. because an ITO is deposited on a heat-sensitive polymer substrate. As a result, a substrate temperature should be low enough (xe2x89xa6150xc2x0 C.) to prevent thermal damage. Therefore, a low temperature deposition technique is the key process in manufacturing optoelectronic devices having an ITO thin film as a conducting electrode.
Conventionally, the ITO thin film was formed on an organic substrate at a low temperature using spray coating, screen coating, or electroless plating. In those techniques, process parameters such as a target composition, a substrate (or processing) temperature, an oxygen partial pressure, and a deposition rate should be controlled to obtain a high optical transmittance and a low resistivity in the ITO thin film. However, all of these films tend to have either a high resistivity or a low optical transmittance. A resistivity and an optical transmittance of the commercially available ITO films are higher than 2xc3x9710xe2x88x924 xcexa9cm and lower than 87% (on glass), respectively. Thus, there is a need to develop a process for forming an ITO thin film having a high transmittance as well as a high electrical conductivity.
Accordingly, the present invention is directed to a method of forming indium tin oxide thin film using a magnetron negative ion sputter source that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for forming an indium tin oxide thin film at a low temperature that has a high transmittance as well as a high electrical conductivity.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from-the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claim hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method for forming an indium tin oxide thin film on a substrate in the present invention includes the steps of introducing a mixture of an inert gas and a low electron affinity element in close proximity to a target as a primary sputter ion beam source, providing an oxygen gas between the target and the substrate, applying an electrical energy to the target to ionize the mixture, confining electrons generated in the ionization in close proximity to a surface of the target facing towards the substrate, disintegrating negatively charged ions from the target, and forming the indium tin oxide thin film on the substrate.
In another aspect of the present invention, a method for forming an indium tin oxide thin film using a sputter system, the method includes the steps of cleaning a substrate in acetone, ethanol, and distilled water sequentially and drying the substrate, placing the substrate in a process chamber, evacuating the process chamber where a sputter action occurs between a target and the substrate, wherein the target has first and second sides, introducing a mixture of argon and cesium to the second surface of the target as a primary sputter ion beam source, wherein the target has at least one through-hole, diffusing the mixture through the through-hole in the target from the second surface to the first surface, providing an oxygen gas between the target and the substrate, maintaining the process chamber to have a constant working pressure, applying an electrical energy to the target to ionize the mixture, confining electrons generated in the ionization in close proximity to the first surface of the target, disintegrating negatively charged ions from the target, and forming the indium tin oxide thin film on the substrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.